This invention relates to photoelectric pulse initiator for utility meter type three wire telemetry and recording systems and more particularly to such pulse initiators having a single track pattern scanned by two optoelectronic sensors.
The use of pulse initiators in utility meters is well known particularly in the field of electric utility metering. Output pulses produced by the pulse initiators are applied through a three wire telemetry system to a receiver which often includes a demand or load survey magnetic recorder. The pulses are generated in response to movement of a utility meter such as a watthour meter which is rotated at a rate corresponding to the consumption of electric power measured by the watthour meter. As disclosed in U.S. pat. Nos. 3,733,493 issued May 15, 1973 and 3,878,391 issued Apr. 15, 1975, both assigned to the assignee of this invention, techniques for detecting rotation of the meter movement include a rotating two track pattern which optically activates two optoelectronic sensors. These sensors are alternately activated to produce impluses which control an output pulse generator. The output pulses are produced as opposite polarity pulses through either of two conductors and a common conductor of a three wire telemetry system.
Important considerations in the manufacturing use of pulse initiators include a simple and low cost unit intended for reliable service under varying operating conditions. An electro-optical pattern and sensing assembly included in the pulse initiators preferably affords flexibility in the choice of different desired pulse rates. These pulse rates are responsive to different predetermined amounts of the quantity measured by the meter as particularly described in the aforementioned U.S. Pat. No. 3,878,391. The patent describes how different pulse energy values are determined with respect to the different revolution per pulse constants associated with each pulse initiator of a watthour meter.
The aforementioned patents are directed to photo-electric pulse initiators having reflective patterns which are rotated by a watthour meter movement. These patterns include two rows of reflecting indicia or segments wherein each row is associated with a separate sensor. Rotation of the two rows of segments produces impulses alternately from the two sensors. This is required in order to produce the self-latching operation of an output pulse generator. The output pulses from one type of generator are produced by a mercury wetted self-latching relay which is operated by opposite directions of impulse current flow to produce the opposite polarity pulses in three wire telemetry systems.
One known alternative to the use of patterns of reflecting segments is the use of a shutter disc which includes slots that periodically pass light between an illuminating source and a photoelectric or radiation responsive sensor. Pulse initiators having shutter discs are disclosed in U.S. Pat. Nos. 3,311,824 issued Mar. 28, 1967 and 3,114,081 issued Dec. 10, 1963. In the U.S. Pat. No. 3,311,824 two shutter discs are described each having a slot pattern for controlling the light from a single illuminating source to two sensors. Alternate impulses are generated in response to the rotation of the two shutter discs by a watthour meter shaft rotation. The use of two discs require additional space over the use at a single disc and the difficulty of orienting the discs precisely relative to each other.
In the U.S. Pat. No. 3,114,081 a single shutter disc is utilized having a single sensor which is exposed to the light exposed through a single slotted disc. The disc slots are formed with both radially and circumferentially extending slot areas intersecting each other. Rotation of the shutter disc effects three different levels of radiation. impinging the sensor. This arrangement requires precise control of different levels of light on a single photo-electric sensor which is used to modulate a current signal having a reference plus more positive and more negative current levels.